States the 2013–2014 California drought was initiated by an anomalous high-amplitude ridge system

Investigates this anomalous ridge using reanalysis data and the Community Earth System Model (CESM)

Finds the ridge emerged from continual sources of Rossby wave energy in the western North Pacific that started in late summer and intensified into winter

Finds the ridge generated a surge of wave energy downwind and deepened further the trough over the northeast U.S., forming a dipole

Says that the dipole and associated circulation pattern is not linked directly with either El Niño–Southern Oscillation (ENSO) or Pacific Decadal Oscillation; instead, it is correlated with a type of ENSO precursor

Finds the connection between the dipole and ENSO precursor has become stronger since the 1970s, and this is attributed to increased greenhouse gas loading as simulated by the CESM

Holds that there is a traceable anthropogenic warming footprint in the enormous intensity of the anomalous ridge during winter 2013–2014 and the associated drought